Many attends have been made to generate a foam or head when dispensing a beverage from a container and when dispensing a beverage from a non-resealable container in particular, use has been made of a secondary chamber located inside the container and in communication with the inside of the container via a small orifice. The secondary chamber is charged with a superatmospheric pressure and is usually in equilibrium, via the orifice, with the contents of the container. When the container is broached so that its internal superatmospheric pressure is suddenly vented, the remaining superatmospheric pressure in the secondary chamber generates a rapid turbulent flow of gas or beverage through the orifice into the beverage inside the container which generates a quantity of gas bubbles which, as they rise through the beverage in the container, seed the creation of further bubbles so resulting in the generation of a required head either on the beverage inside the container or on the beverage as it is dispensed from the container by pouring into a glass or other receptacle.
GB-A-1266351 describes an early, not commercially successful system using a secondary chamber in which the secondary chamber is charged with gas as part of an initial filling or subsequent pressurising step. In an alternative described in GB-A-2183592 the pressure in the container builds up after it is sealed and as a result the beverage from the container enters the secondary chamber via the small orifice.
The packaging of a beverage in a container, particularly a carbonated beverage should maintain the beverage out of contact with oxygen. The presence of oxygen inside the container leads to the beverage being oxidised with a resulting impairment of flavour and risk of microbial growth leading to, for example, acetification of the resulting beverage when it contains alcohol. Thus, there is a general requirement to displace substantially all of the oxygen from a container, and its secondary chamber, when this is used, before the container is sealed. When the secondary chamber has the form of a hollow insert with only a small orifice in its wall and this insert is filled with air it is difficult to displace all of the air during the filling and sealing of such a container.
As a way of overcoming this problem GB-A-2183592 describes manufacturing such a secondary chamber by a blow moulding technique using an inert gas to form the secondary chamber and then only forming the orifice as the secondary chamber is placed into the container, for example by irradiation with a laser beam. However, in practice, this is not the way that such containers are filled. In practice, the secondary chamber is injection moulded and has its small orifice formed in its wall. After its formation, the normal atmospheric gases diffuse into and fill the secondary chamber. Such a secondary chamber is then inserted into an empty container and the whole is subjected to a reduced pressure, filled with an unoxidising gas such as carbon dioxide, nitrogen, or a mixture of these, and evacuated again to flush substantially all of the oxygen from both the inside of the container and the inside of the secondary chamber before the container is filled with beverage. In this way the amount of oxygen remaining in the sealed container is reduced to an acceptable level but these additional evacuation and flushing steps add a considerable delay and difficulty to the container filling stage with the result that the speed of filling is reduced to about 25 per cent of that in systems in which a secondary chamber is not included in the container